Organic Light-Emitting Diodes (OLEDs) are regarded as the most promising components for flat panel display, and meanwhile are considered as the components that are most likely to implement flexible display components.
An OLED generally includes an anode, a cathode, a light-emitting layer, a hole transport layer and an electron transport layer, and when power supply reaches an appropriate voltage, the applied voltage drives electrons and holes to inject into the electron transport layer and the hole transport layer from the cathode and anode, respectively. The electrons and holes meet and combine during transmission, i.e., the so-called electron-hole recombination occurs, to generate photons. Holes at the anode and electrons at the cathode will combine in the light-emitting layer to emit light.
Currently, the service life of the OLED restrains industrialization thereof. When electrons are injected into the electron transport layer from the cathode during operation of the OLED, in order to increase the number of the injected carriers and improve luminous efficiency, the cathode of the OLED is made from a material with a similar work function as the light-emitting layer to reduce the energy barrier. However, such material having a low work function (e.g., magnesium, aluminum, silver, etc.) is generally reactive metal material and is very prone to react with water and oxygen in the external environment to disable the OLED. Meanwhile, the hole transport layer and the electron transport layer are easily eroded by water and oxygen, resulting in damaged pixels and shortened service life of the component. Therefore, packaging technique for OLED is particularly important. Effective packaging can prevent water vapor and oxygen from invading, prevent organic material from ageing and prolong the service life of the OLED.
In practical operation, the operation of the OLED will be badly influenced even when 10% of the cathode thereof is eroded, and similarly, a flexible OLED also needs to be packaged. At present, there are mainly two packaging techniques for OLEDs, namely, cover plate packaging and film packaging. For the cover plate packaging, glass cover plate material is mainly employed, which leads to relatively large thickness and relatively tightened sealing, however, the glass cover plate packaging can hardly satisfy the bendability of a flexible OLED. For the film packaging, film material is mainly employed, which leads to relatively small thickness and good flexibility, and is therefore commonly used for packaging a flexible OLED. The film packaging includes single-layer film packaging and multilayer film packaging, and in order to achieve a packaging effect comparable to that of the glass cover plate packaging, a flexible OLED often employs a multilayer film packaging structure. As shown in FIG. 1, the flexible OLED 6 employs a multiplayer film packaging structure in which inorganic material film layers 4 and organic material film layers 5 are laminated alternately. The inorganic material film layer 4 can prevent water vapor in the external environment from invading into the inside of the flexible OLED 6, and the organic material film layer 5 has good flexibility and can enhance the overall flexibility of the multilayer film packaging structure.
The multilayer film packaging structure typically has a relatively large thickness (can reach a couple of microns), due to the influence of stress and defect, the inorganic material film layer 4 is likely to crack when the flexible OLED display component is bent. For example, because of a crack or pinhole existing inside the inorganic material film layer 4 and stress mismatch between the inorganic material film layer 4 and adjacent organic material film layer 5 when they are in contact with each other, the inorganic material film layer 4 is very likely to crack along the position of the defect (e.g., crack or pinhole) when the packaging structure is bent along with the flexible OLED display component, which makes the bendability of the packaging component of the flexible OLED unsatisfactory.